This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. PTPMT1 was the first protein tyrosine phosphatase found to localize to the inner membrane of mitochondria. Our recent work has suggested that PTPMT1 is required for the integrity and optimal function of mitochondria. We collaborate with NCMIR whose researchers perform electron microscopy and electron tomography to further characterize the function of PTPMT1 in mitochondria.